The invention relates to the measurement and, in some circumstances, compensation of a signal delay introduced by circuitry, such as between reference signals and feed-back signals in a closed-loop configuration of electronic circuitry such as, but not limited to, radio transmitters.
There is often a need to estimate an amount of delay introduced by circuitry. Taking modern wireless transmitters as one of many possible examples (e.g., wireless transmitters in mobile phones, or in computers with built-in transceivers) knowledge of the transmitter's delay (i.e., between input and output) may be an integral part of techniques applied to make any of a number of types of measurements in a closed-loop configuration. Different types of measurements can be made with such a configuration, such as (without limitation):                1. Transmitter Power measurement        2. Transmitter Gain measurement (fast power measurement)        3. Transmitter Phase measurement        4. Transmitter IQ Mismatches (i.e., mismatches between amplitude and/or phase of an In-phase and Quadrature-phase signal pair)        5. Transmitter Adaptive Digital Pre-distortion        
It is very important that an accurate measurement of the delay (“loop-back delay”) be made. The feed-back signal, herein referred to as SFB(t), is a delayed but accurate copy of the base-band transmitted signal. This delay will vary with process, transmitter settings, temperature, and the like.
The loop-back delay can severely degrade the closed-loop measurement if not compensated for. This is especially so in those algorithms that operate on a sample-by-sample basis.
Because the loop-back delay is not known a-priori with sufficient accuracy, a calibration algorithm is required.